Ships and submarines are powered by steam and combustion turbine propulsion systems. Large reduction gears transfer rotational work from the turbines to the drive shafts rotating the ship propellers. These gears require a voluminous flow of lubricating oil. Oil is also used to lubricate the prime mover bearings and other components of the propulsion system.
A marine propulsion system must always have an adequate amount of lubrication oil being supplied to its gears, bearings and other components. To properly lubricate gears and bearings, the oil must form a thin film between the gear teeth and bearing surfaces. The oil film prevents opposing metal surfaces from coming into contact with each other. By preventing metal-to-metal contact, the lubricating oil film protects the metal surface from wear and other harmful effects. The oil also act as a coolant for the gears, bearings and other components of the propulsion system. The oil removes heat as it flows through the propulsion system.
An insufficient amount of lubricating oil can cause the reduction gears, bearings and other components to wear at unacceptably high rates. An inadequate amount of oil may result in excessive frictional heating of the propulsion system. A complete lack of oil can cause the gears and bearings to seize or otherwise fail.
The amount of oil necessary to lubricate a propulsion system varies with the operating condition of the system. When a ship or submarine is traveling at high speed its propeller and turbines are also rotating at high speeds. The forces transmitted from the turbines by the reduction gears to the propeller shafts are greatest when the ship or submarine is moving fast. High rotation speeds in the propulsion system and large forces in the reduction gears require large volumes of lubricating oil at relatively high pressure.
As shown in FIG. 3, the flow demand for lubricating oil increases as the speed of the ship increases. At slow speeds, the propulsion system requires much less oil than it requires at high speeds. Accordingly, the volume of oil needed varies greatly with the operation of the ship.
To provide an adequate supply of oil at all operating conditions, conventional lubricating system are sized to constantly provide the maximum volume of oil. Conventional lubricating systems employ single speed motor driven positive displacement pumps. These pumps are extremely reliable but deliver oil at a constant rate. For a constant supply of oil to satisfy a varying demand for lubricating oil, the supply must be at the level of maximum demand. Thus, pumps in conventional systems constantly provide oil at the maximum operational demand of the propulsion system.
Conventional lubricating systems with single speed pumps circulate oil through the reduction gears, bearings and other propulsion components at a uniform pressure and volume corresponding to the maximum demand for oil. When the propulsion system does not require the maximum amount of oil, then the amount of lubricating oil supplied to the propulsion system is excessive.
Continually providing the maximum rate of oil results in a considerable mismatch between the demand and supply of oil. The excessive supply of oil flowing through the propulsion system increases the losses of the components in the propulsion and lubrication systems. In addition, the lubricating system is noisy when operating at maximum capacity. Since it is always operating at maximum capacity, the lubrication system is always noisy.
To regulate the amount of oil circulating through the propulsion system, some conventional lubrication systems include an oil recirculator. The recirculator accommodates excessive oil flow when the propulsion system does not require a maximum volume of oil. Even with a recirculator, the oil pump operates a constant maximum rate. But, the recirculator keeps some of the oil from flowing to the propulsion system. Oil not needed by the reduction gears, bearings and other components is diverted into the recirculator. When the load on the propulsion system decreases, the volume of lubrication oil circulating through the system is correspondingly reduced and the volume flowing into the recirculator increases.
An oil recirculator mitigates some of the losses and other harmful effects caused by constantly circulating large amounts of oil through the propulsion system. Noise is not reduced by a recirculator. Pump noise remains high because the pump is still operating at a maximum state. In addition, the recirculator itself increases the noise level of the lubrication system.
Two speed positive displacement pumps have been used for single speed pumps to more closely match the lubrication requirements of the propulsion system than does a single speed pump. Two speed pumps supply lubricating oil at two flow rates--a maximum rate and an intermediate rate. The maximum rate satisfies the maximum demand for lubricating oil made by the propulsion system. The intermediate rate provides an adequate amount of lubrication oil when the propulsion system is operating at or below a preselected intermediate power level. The advantage of a two-speed pump is that it is not always operating at a maximum speed. At or below the preselected propulsion power level, the oil pump is operating at an intermediate capacity that is quieter and less wearing on the lubrication and propulsion system than is the maximum capacity of the pump.
The lubrication requirements of a ship's propulsion system is shown in FIG. 3. The volume of lubricant required by the propulsion system increases with the speed of the ship as shown by dotted line 1. At maximum speed, the propulsion always operating at a maximum speed. At or below the preselected propulsion power level, the oil pump is operating at an intermediate capacity that is quieter and less wearing on the lubrication and propulsion system than is the maximum capacity of the pump.
The lubrication requirements of a ship's propulsion system is shown in FIG. 3. The volume of lubricant required by the propulsion system increases with the speed of the ship as shown by dotted line 1. At maximum speed, the propulsion system requires a maximum volume of lubrication. A single speed pump constantly supplies this maximum amount of oil for all ship speeds as is shown by line 2. As shown by dotted line 3, a two-speed pump provides the maximum oil flow when the propulsion system is operating above a predetermined speed level 4 and a lower volume of oil when the propulsion system is operating below this level. As can be seen from FIG. 3, the lubrication oil flow provided by one-and two-speed pumps does not closely track the volume of oil 1 required by the propulsion system. With both types of pumps, a great deal more lubrication oil is supplied than is demanded by the propulsion system. This excess oil supply increases noise and causes unnecessary wear in the system.
The present invention is a variable speed lubrication pump controlled by a microprocessor. The discharge flow rate and pressure of the oil pump varies with it speed. The microprocessor adjusts the rate of oil supplied by the pump to closely track the amount of oil required by the propulsion system. As shown by the variable oil supply line 5 in FIG. 3, the supply of lubrication oil tracks the demand for oil, but is always slightly greater than the demand. The lubrication system adapts to the demand for lubricant.
The microprocessor control is programmed with algorithms and/or tables that correlate the operating condition of the propulsion system, to the amount of lubrication oil required by the propulsion system. Methods for programming microprocessors are well known. The microprocessor receives signals from sensors indicative of the rotational speed of the propulsion turbine, the setting of the propulsion turbine control valve, the throttle setting forth the propulsion system, the speed of the ship and the speed of the lubrication pump and possibly other information. With this information, the microprocessor calculates whether the variable speed pump should rotate faster, slower or hold a constant speed. In this way, the lubrication flow to the propulsion system is continually adjusted to a level slightly above the volume of lubrication needed by the propulsion system.
The adaptive lubrication oil system of the present invention may also include a two-stage pump. Such pumps are most useful in propulsion systems that have a combined lubrication and hydraulic oil system. Hydraulic oil must often be provided at pressures much greater than that demanded of lubrication oil. A two-stage pump has a high pressure discharge providing oil to the hydraulic system and a low speed discharge providing oil to the lubrication system.
For a conventional single speed pump to supply oil to a combined lubrication and hydraulic system would require the pump to continuously provide oil to both systems at the maximum pressure needed by the hydraulic system. Such a conventional system would be exceedingly noisy and may have many other undesirable effects. Substituting a two-speed pump would reduce but not eliminate these undesirable effects.
A two-pressure, variable speed pump satisfies the requirements for a combined system lubrication and hydraulic system without creating extra noise or supplying high pressure oil where it is not needed. A microprocessor can monitor the demands for high and low pressure oil and adjust the operation of the pump accordingly.